Existing hot water systems are common place in most societies as a means for providing on-demand hot water for cooking, cleaning, bathing and space heating, etc. These existing hot water system rely on thermodynamic processes for transferring heat energy from a heat energy source to water, thereby heating the water when needed. The energy source(s) typically consist of an on-demand heat source that use energy sources such as fossil fuels or electricity to heat the water.
While these hot water systems are useful, they are not without safety issues. The risk of incubating bacteria colonies in these hot water systems remains high. For example, the presence of Legionella bacteria, e.g., Legionella pneumophila, in hot water systems is a common problem in which Legionella pneumonia can cause a potentially fatal respiratory disease in humans. To address the problem of bacterial growth in hot water systems, some existing hot water systems perform a temperature pasteurization cycle of water tanks and pipes on a set schedule by triggering an on-demand heat source, e.g., boiler, to begin heating water to a set temperature for a predetermined period of time. Pasteurization heats fluid below its boiling point at temperature(s) that kill harmful microbes and waterborne pathogens. Typically, the scheduled pasteurization cycle of the hot water system will occur according to a preconfigured schedule.
In some cases, however, setting a hot water system to perform the pasteurization cycle on a set schedule waste energy. For example, a system having more than one heat source may waste heat recovery. In particular, if one heat source is solar or a biomass boiler, for example, the water may sometimes reach temperatures that pasteurize the water without running a pasteurization cycle. In other words, adhering to a set pasteurization cycle schedule may lead to situations where the water in the hot water system was pasteurized a day earlier due to an increase in solar energy collection, but the hot water system may nevertheless trigger an on-demand heating source to begin the pasteurization cycle even though pasteurization is not required for several more days.
In another situation, the water in the hot water system may reach temperatures close to the required pasteurization temperature during the middle of the week. However, the pasteurization cycle may not be set to begin for another several days, thereby preventing the hot water system from taking advantage of the fact that only a fraction of the typically heat energy needed for pasteurization will be needed to heat to the water to the required pasteurization temperature. Such a situation may occur if the variable heat source, e.g., solar based heat source, has already heated the water close to the required pasteurization temperature. Therefore, while existing hot water systems help reduce the risk of incubating bacteria colonies in hot water systems, these existing hot water systems do so in an inefficient manner that wastes energy resources and increases the cost of operating the system.